The invention relates to protective helmets and more particularly to protective helmets having an energy-absorbing foam liner or shell therein.
Head injury is a significant cause of accidental death and disability among children and adults in the United States and other countries, frequently resulting from activities such as bicycling, skiing, horseback riding, skateboarding, snowboarding, ice skating, rollerskating, and in-line skating. In general, head injuries fall into two main categories-focal and diffuse. Focal injuries are limited to the area of impact, and include contusions, hematomas, lacerations and fractures. Diffuse brain injuries involve trauma to the neural and vascular elements of the brain at the microscopic level. The effect of such diffuse damage may vary from a completely reversible injury, such as a mild concussion, to prolonged coma and death.
In recent years, two-thirds of all bicycle-related deaths involved head injuries. A 1993 study by the Consumer Product Safety Commission found that about 18% of bicyclists wear helmets. Research has shown that helmets may reduce the risk of head injury to bicyclists by 85%.
There are three general categories of protective helmets used by sporting participants.
1. Hard shell helmets having a hard outer shell, typically made of a thermoplastic material such as polycarbonate or ABS, an inner shell or energy-absorbing liner made of expanded polystyrene (EPS) or expanded polypropylene (EPP), and optionally a comfort liner or comfort pads of flexible foam inside the EPS liner.
2. Foam helmets made of a thick layer of EPS or EPP with no outer shell and optionally a comfort liner or comfort pads inside.
3. Microshell helmets having a thin outer microshell (0.2-0.5 mm thick) made of a thermoplastic vacuum-shaped material such as polyethylene over a relatively thicker inner shell or liner of EPS or EPP and an optional comfort liner or comfort pads.
EPS consists of plastic cells that have been bonded together in the shape of a helmet during the molding process. When subjected to an impact, the cells of an EPS helmet will xe2x80x9ccrushxe2x80x9d, or permanently deform, thereby protecting the wearer by attenuating the energy of the impact. However, the EPS helmet liners are rigid, inelastic, with very little flexibility. Because of this, they are xe2x80x9csingle impactxe2x80x9d helmets, and have serious deficiencies in their energy attenuation characteristics.
Prior art protective helmets include those described in U.S. Pat. Nos. 5,088,130; 5,298,208; 5,943,706; 6,070,271; 6,154,889, the entire contents of which are incorporated herein by reference in their entirety.
There is a need for an energy-absorbing foam liner which more effectively provides protection to the wearer of a protective helmet.
A protective helmet is provided comprising an energy-absorbing shell. A substantial portion of the energy-absorbing shell is viscoelastic foam. The helmet preferably includes a resin outer shell. The viscoelastic foam is compression rate sensitive.